Antioxidants are added to lube oils to neutralize or minimize oil degradation chemistry. For example, U.S. Pat. No. 5,200,101 discloses certain amine/hindered phenol, acid anhydride and thiol ester-derived products are multi-functional antioxidant, antiwear and rust inhibiting lube additives.
The combination of a metallic dithiophosphate hydroperoxide decomposer and aminic antioxidant is reported to have a synergistic effect on lubricant antioxidant performance. See Maleville et al, Lubrication Science, V9, No. 1, pg. 3-60 (1996). Sulfur-substituted derivatives of mercapto carboxylic esters also are reported to posses antioxidant properties. See M. A. Mirozopeva et al., Naftekhimiya, V28, No. 6, pg. 831-837 (1988). There remains a need, nonetheless, for improved lubricant additives and lubricant compositions containing them.